The central theme of this subproject is the assessment of aspects of vestibular performance that are functionally significant to normal subjects and patients. Traditional tests are not conducted under natural conditions and thus may not be reflective of the systems true mechanisms. This subproject has four specific aims. First the angular and linear vestibulo-ocular reflexes and visual vestibular interaction will be quantified during walking, standing, and running conditions in normal subjects and patients with vestibular syndromes. Second, eccentric rotation tests of otolithic function will be developed that combine linear acceleration with angular rotations in pitch and yaw. Third, the VOR initiation in both yaw and pitch will be evaluate as a functional vestibular test. Fourth, tests of dynamic visual acuity will be developed as an index of vestibular performance during gaze stabilization. Magnetic search coil and flux gate sensors will be used to make precise measurements of eye and head movements. Effects of aging, peripheral vestibular loss and cerebellar dysfunction will be assessed on these reflexes.